Colored steel



`Mary 27, 1941., c. BA'vrcHELLER COLORED STEEL Filed June 30, 1938 Patented May 27, 1941 COLORED STEEL Clements atcheller, Glens Falls, N. Y., assignorv to Allegheny Ludlum Steel Corporation, a corporation of Pennsylvania 1, Application June 30, 1938, Serial No. 216,719

9 Claims.

My invention relates to the surface coloration of stainless steels and particularly to the production of patterns thereon of distinctive color which may be purely decorative or of a utilitarian nature such as signs, badges, name plates, license plates or the like.

In my copending applications Serial No. 206,043 led May 4, 1938, and Serial Nos. 241,991 and 241,922 filed November 23, 1938 I have disclosed methods of producing coherent and tenaciously adherent color lms on the surfaces of articles formed of stainless steel containing 7% or more by weight of chromium, or at least a sufficient 1 quantity of chromium to permit the steel to be treated in accordance with my processes without destructive etching of the surface thereof. These'polor lms although extremely thin are very permanent in character and, due to their thinness, have a surface nish or texture substantially identical with thesurface finish of the steel to which they are applied. That is to say, if the surface of the stainless steel is highly polished, the film produced directly by my treatment is highly polished. Similarly, if the surface of the stainless steel is pickled, then the surface of the color lm is characteristic of a pickled surface except for the color.

Panels or trim of stainless steel having a unifarm surface color throughout, either' of the natural metal or as uniformly colored by my particularly when of large area, and one of the objects of my invention therefore is to provide a simple method whereby such stainless steel surfaces may be treated to form thereon or therein decorative patterns in which the pattern and the background haveV distinctive colorations. 'I'he samel method used in producing a purely decorative effect in which the utility of the finished article lies largely in its aesthetic characteristlcs may also be used in the production of'signs, name plates, license plates, badges and the like having, in addition to aesthetic properties, great practical utility because of the permanence of the article. It is therefore to be understood `that the objects of my invention include the production of such articles. l

I accomplish the foregoing and-otherobjects by the method described below and illustrated in the accompanying drawing in Which- Y Fig. 1 is a plan view of a mask or stencil of a simple design;

Fig. 2 is a section of Fig. 1 in the plane 2--2;

Fig. 3 is a plan view of a surface of stainless and in which the mask or stencil shown in Fig. 1 is' used;

Fig. 4 is a plan view of the stainless steel article shownA in Fig. 3 which has been treated by a modification of the process used in producing the article of Fig. 3;

Fig. 5 is a highly magnified section of Fig. 3 in the plane 5 5;

Fig. 6 is a highly magnified section of Fig. 4 in the plane 6 6; and

Fig. '7 is a front view of a stainless steel sign or name plate produced by my process.

In carrying out my invention, I first color the surface of the steel throughout by subjecting it to the action of an oxidizing agent for a sufcient length of time to produce thereon or therein a coherent and tenaciously adherent color lm. The agent employed should be of such character as to produce this lm without etching or in any way otherwise affecting the surface finish of the steel. That is to say, if the steel is highly polished, the oxidizing agent employed should be so adjusted that this surface is not affected in any way other than to produce a color thereon or therein.

It is to be understood that the pattern produced on the steel may be in color on the natural steel background or of the natural steel color on a colored background, or the pattern and the background may be both colored by my process but to different color or tone values.

In my copending application Serial No. 206,043 I have described a method of coloring the surface of a stainless steel by immersing the same in a solution of the following composition-v Formula 1 Parts by weight Etching inhibitor 4-25 Sulphuric acid (1.84 sp. gr.) 23-54 Water 35-64 In the above formula it will be noted that the acid concentration in the *sulphuric acid-water solution varies from 23 parts ln a total of 87 parts (23+64), to 54 parts in a total of 89 parts (544-35), or from about 26% to about 61%.

By heating the above solution and maintaining it within Va temperature range of about F. to 200 F. a specimen of polished stainless steel of the 18-8 type (18 Cr, 8 Ni) or a straight 17-8 chromium type when immersed therein for a period of about one hour will acquire a color running from a light yellow gold through the bronzes and darker browns up to a deep, jet black, depending principally upon the duration of the treatment, the acid concentration in the solution, its temperature, and the presence or absence of alloying elements in the steel other than chromium.

Where a jet back color is desired, I prefer to use the ingredients in the above formula within the following limits- Formula 2 Parts by weight Etching inhibitor -14 Sulphuric acid (1.84 sp. gr.) 36-50 Water 30-50 In the above formula it will be noted that the acid concentration in the sulphuric acid-water solution varies from 36 parts'in a total of 86 parts (364-50), to 50 parts in a total of 80 parts (50+30), or from about 42% to about 63%..

The color build up is very gradual during the earlier stages of the processing but prograsses very rapidly during the last few minutes up to what is apparently its maximum color and film depth. y

When the temperature of the solution is permitted to approach the boiling point, which is around 250 F. 'to 260 F., the rate of color depition ls so extremely rapid that the film formed is neither coherent nor adherent. Furthermore,

the surface of the steel may be destructivelyv Moreover, a much longer time is necessary in this case to produce the color.

While I have indicated .that the temperature of the treating solution should be maintained between about 185 F. and 200 F., because this is the best temperature to produce rapidly and economically a permanent deep black color with my preferred formula above, a comparablev result can be obtained by treating the steel in a solution at normal room temperature. In this case, however, the time necessary to produce a black color lm of equivalent thickness to that produced by my preferred treatment requires many hours. Solutions at a temperature of say 70 F. are therefore workable but their commercial practicability may be open to question because of the long time factor.

As an etching inhibitor in the above formula, I prefer to use ammonium dichromate, although other chromium salts such as sodium dichromate, potassium dichromate or even chromium trioxide, either alone or\in combination with each other or with ammonium dichromate form vsatisfactory inhibitors.

Where i-t is desired to produce color lm of less sintensity, such as a light yellow gold, a bronze, or a brown film, I may use the following solution:

In the above formula it will be noted that the acid concentration in the sulphuric acid-water solution varies from-.r para in a total of so rs 2,24a,revA

parts (7-1-23), to 11 parts in a total of 30 parts (151+I19) or from about 23% to about 37%.

The time required to form these lighter color lms at the preferred treating temperature lof from 185 F. to 200 F., however, is somewhat longer than that required to produce the black films with a higher acid concentration. Moreover, these lms are considerably less in thickness than the black lms.

Where it is desired to produce a color more closely resembling the color of true gold than can be produced by the above formulae, I use, as an inhibitor in my acid solution, a salt of the metal vanadium in place of the chromium. as described in my copending application aforesaid Serial No. 241,992. In such a case, I prefer to use a solution of the following order:

Water 35-70 (Water should be preferably free of iron and lime.)

Other vanadium compounds, such as ammonium vanadate (ortho) or vanadic acid (vanadium pentoxide) when used as inhibitors produce fairly satisfactory gold tones, but the results seem to be more consistent when ammonium meta vanadate is employed.

i1`he procedure followed in producing gold tones by the use of Formula4 is the same as described above in connection with the other formulae and it may be noted that these color lms can be produced from room temperature solutions in about to 150 hours where time is not an important factor.

Where the pattern to be impard to the steel is to appear in the natural color of the steel surface, I prepare a mask or stencil having cut-out portions corresponding to the desired pattern.

Any suitable sheet material may be used for forming the mask or stencil, as. for example,

any of 'the well known masking papers now on the market in which the pattern may be cut out. One proprietary article which I have found very satisfactory for my .Purpose is sold under the trade name Scotch tape, and is provided with an adhesive on one side whereby it may be temporarily adhered to the surface of the steel.

In Fig. 1 of the drawing, I have shown a mask or stencil l having cut-'out portions 2 and a layer of adhesive 3 on the back thereof. The stencil shown is adapted for use in forming a rectangular border on a panelof stainless steel colored as above described.

The stencil or mask is superimposed on the colored surface of the steel to which the pattern. is to be imparted and mus-t be held or otherwise secured in xed relation thereto during Ythe buiiing operation hereinafter described. Preferably, but not necessarily, it is adhesively secured to the colored surface of the steel.' I'he color in or on those portions of the steel which are exposed through the cut-outs in themask is then removed by applying thereto a simple bumng wheel or roll carrying `upon its surface a grit or rouge of such abrasive properties as will fairly quickly and completely grind or buff out the color and produce the desired nish on these portions of the steel. After such bumng operation is completed, it is simply necessary to remove the mask to find that the exposed portion of the colored metal is now in its original color, as shown at 4, while the' colored areas which have been protected by the mask are completely intact, as indicated at and 6. The small zones of color which remain because they were covered by the connectors I0 in the mask can be buied off after the removal of the mask.

It seems obvious that the above. `process may be slightly modified by adhering, or otherwise holding in fixed relation, to the surface of the colored steel, a rectangular frame-like mask such as might be represented by the cut-outs 2 and bufng the color from the surface of the steel around the mask. In this case, when the mask is removed, the color pattern thereunder will be found intact and the background will be the ori-ginal stainless steel.

By the additional step, hereinafter described, it is possible to produce a two color effect.

After removing the mask and thoroughly cleaning' the surface of the steel, it may again be immersed in any of the above solutions, for a sufficient period of time, to produce upon those portions of the surface where t'he original color has been buffed out a color of lighter tone value. For example, a bright gold 'tone may be imparted to the buied portions by using Formula. d having ammonium met-a vanadate as an inhibitor. While this secondary vcolor step may deposit a superposed very thin lm over those portions of the steel surface Whioh'have already been colored, the resulting' effect is so slight as not materially to eiect its original appearance.

My invention will be found extremely valuable in its adaptability to produce very rapidly and inexpensively extremely attractive signs, tablets and the like by simply using a piece of highly polished stainless steel bolored by my process and using stock cut-out letters, patterns and the like to produce thereon an unlimited variety of designs.

As stated above, the surface nish or texture of the colored portions conforms to the surf-ace texture or finish of the steel to which the color is applied. Hence, if it is desired to produce, for exemple, a dull colored background or dull colored letters or patterns, the surface of the stainless steel may, before coloring, be given a slight acid pickle or even an electro-etch to reduce its surface from the characteristiccold rolled planish to a uniformly dull surface. When a specimen so treated is colored and the portions exposed through the mask are polished as above described, it is pos-sible to produce highly polished buffed letters or patterns on a. dull background or dull letters or patterns on a highly polished background.

The color films produced by my process are substantially integral with the steel and therefore do not peel, crack or craze. Microchemical tests andspectrographic analyses show the presence in the films of oxides both chromium and iron, and their thickness, determined by calculations from their interference colors, does not exceed about 1500 Angstrom units. Due to the extreme .thinness of the film ofcolor, those zones where it is buied off are not Derceptibly lower than the colored zones and it is quite impossible, either by eye or by touch, to detect any difference in elevation of these zones. The surface of the steel seems perfectly smooth throughthat the words which I have used are words of description rather than of limitation. Hence, changes within the purview of the appended claims may be made without departing from the true scopey and spirit of my 'invention in its broader aspects.

'What I claim is: i 1. .'Ihe method of forming a design on a surface of stainless steel which comprises, subjecting' said surface to the action ofan oxidizing agent to product an adherent and coherent. colored film thereon, masking those zones of lsaid colored surface `which are to be preserved in the finished design, removing those portions of said film which are exposed, and subjecting said surface again to lan oxidizing agent for a suflicient length of time to form on those portions thereof from which the dirst iilm was removed a second film having a color tone differing from that of the balance of said surface.

2. The method of forming a design on a surface of stainless steel which comprises subjecting said surface to the action of a solution containing sulphuric acid, Water and an etching inhibitor yfor a sucient length of time to color the same, masking those zones of said colored surface which are to be preserved in the iinishing design,

removing the color from the unmasked zones,

unmasking the masked zones, and thereafter again subjecting said surface to the action of said solution for a period of time sumcient to effect a coloration of those zones from which the original color was removed.

3. The method of forming a design on the surf-ace of stainless steel which comprises subjecting said surface to the action off a solution containing sulphuric acid, water and an etching inhibitor selected from the group-ammonium dichromate,l sodium dichromate, potassium clichromate, chromium trioxide, for a sufficient length of time to color the same, masking those zones of said surfaces which are to .be preserved in said design lwhen the color is removed from the exposed zones about said masked zones, removing the color from said exposed zones, un'- masking said masked zones, and thereafter subjecting saidsurface to the action of a solution containing sulphuric acid, ammonium meta vanaclate and Water for a period of time suiiicient to impart a gold color tone to those zones from which the 'original color was removed.

d. The method of vforming a design on a surface of stainless steel which comprises subjectrl ing said surface to the action `of a solution` containing, by weight,- from about 35 to about 6e parts of water, from about 23 to about 54 parts of sulphuric acid, Iand from about 4 to about 25 parts'of an etching inhibitor at a temperature of from about F. to about 200 F. for a sufiicient length of timeto color the same, masking certain zones of said surface to produce said design when the color is removed from the exposed zones about said masked zones, removing the color from said exposed zones, unmasking said masked zones, and thereafter subjecting said surface to the action of a solution containing, by

weight, from 4 to 30 par-ts of ammonium meta vanadate, from 20 to 60 parts of sulphuric acid,

and from 35 to 70 parts of water for a period of inhibitor in which the sulphur-ic afcid constitutes Amore than 35% and less than 60% of 'the combined weight of the acid and Water, for a sucient length of time to form a. uniform, substantially .black color lm integral with the surface of said steel, masking certain zones of said colored surface in which it is desired 'to preserve the color to produce the design when the color is removed |from the exposed zones about said masked zones, and thereafter removing the 10 aliens? 7. The method set forth in claim 5 -in which the etching inhibitor is selected from 'the groupammonium dichromate, sodium dichromate, potassium di-c'hromete and chromium trioxide.

8. .The method set forth in claim 5 in which the color is removed from the exposed zones by abrasion.

9. The method set forth in claim 5 in which the inhibitor is selected from the group-Jammonium dichromate, sodium dichromate, potassium dichromate land chromium trioxide and in which the solution is employed at a temperature in excess of 175 F. 4but substantially below its boiling point.

CLEMENTS BATCHELLER.

. CERTECATE OF CORRECTION.

Patent No. 2,2538?. v l May 2T, 19in.

CLEMENTS BATCHELLER. .It is hereby certified tht -error appeers inthe printed speeification of the above numbered patentrequiring; correction as follows: Page/v5, second Column, line ll, claim'l, for the Word "produort" read --produce; line 2T, elaim 2, for "finishing" read -finished; line )42, claim 5, Afor nsur-- faces" read surface and that the said Letters Patent should be read with this correction thereinthat the same fnay conform to the record of the oase in the Patent Office.

Signed and sealed this 22nd day of July, A. D. 19M.

Henry Van -Ar sdale (Seal)' Acting Commissioner ofA Patents;- 

